The present invention relates to a generating apparatus and a motor control apparatus.
Load dump surge signifies an abnormally high voltage occurring when a battery or other electric loads connected to a generator are abruptly released despite generating operation still at work resulting in closer to no load on the generator. This abnormally high voltage, if left uncontrolled, is likely to damage other devices connected to the generator. As measures against such danger it is known that, as described in the official gazettes, Japanese Application Patent Laid-Open Publication Nos. Hei 02-197299, Hei 02-197300, and 2003-79195, a zener diode is placed across the generator in order to clamp this high voltage.
A zener diode placed across the generator, for preventing a load dump surge, has been required to be large enough in heat capacity to absorb the energy obtained by calculating the product of the clamping voltage, the current through the zener diode and the load dump surge duration.
Recently, attempts have been made to assemble integrally a generator and its control board together. For this purpose it is necessary to minimize the size of the control board.
A zener diode placed across a generator, though capable of clamping a high voltage, cannot shorten its duration, posing difficulty in replacing it with another one smaller in heat capacity. This has been a problem in minimizing the size of the control board.
Also with a motor control apparatus for a motor having a field coil, there is the following problem. That is, the motor may become a generator-operation state when the motor is conversely driven by an external load (for example internal combustion engine). As this condition raises the direct current voltage, the inverter must be stopped in order to prevent any damage on devices. However, even if stopping the inverter, there is a problem that the field current is gradually attenuated, resulting in the generator still being at work.
There are also previously known systems in which, after starting an internal combustion engine by operating a motor generator (M/G) as its motor (its starter), this M/G is used as a generator. But in the systems, at the time of switching from motoring mode to generator mode, the revolution of the generator may fall, as a result, leading to a fall in the revolution of the engine, and resulting in giving a strange sensation to the operator.